An imaging device used in a cellular phone, a digital still camera or the like is mounted with an optical lens for imaging. As for such an optical lens, an organic-inorganic hybrid lens (hereinafter simply referred to as a “hybrid lens”) which is composed of a glass, a thermoplastic resin or the like or is obtained by forming a thermoplastic resin composition into a lens shape on a glass substrate has been conventionally used. However, since the glass lens is expensive, a thermoplastic resin lens or a hybrid lens is recently predominating (see, Japanese Patent No. 3,926,380).
In mounting an imaging device using such a lens on a printed board, as the method usually employed for connecting these two members (method for mounting the imaging device), a method of connecting using a socket pin or a method of previously soldering an imaging elemental device (a device after removing an optical lens unit from an imaging device) on a substrate and then mounting an optical lens unit may be mentioned. Such methods are taken so as to avoid a problem that the thermoplastic resin as a lens material is deformed due to heat during solder reflow.
However, with recent widespread penetration of a cellular phone with an imaging device, for the purpose of enabling more inexpensive and higher-volume production, a system of mounting an imaging device with an optical lens unit en bloc by solder reflow is demanded. The conventional optical lens using a thermoplastic resin as the lens material cannot meet this requirement, because there is a problem that, as described above, the resin deforms due to heat during solder reflow.
Accordingly, studies are being made on whether an imaging device (with an optical lens unit) can be mounted en bloc by a reflow system as described above by using a thermosetting resin as the lens material. Also, use of a thermosetting resin not only for a lens but also for a transparent protective plate of an imaging device or for adhesion or the like of such an optical component is being studied.
For example, since a thermosetting silicone resin is transparent and less liable to heat discoloration, its application to the usage above may be expected. However, the silicon resin generally exhibits low adherence to glass or the like, making difficult its application, for example, to a hybrid lens. Also, because of its low glass transition temperature and large thermal expansion coefficient, it may be caused to undergo the heat shrinkage due to heat in the use environment and lower the optical properties.
Furthermore, for example, it is possible to obtain a molded article having high heat resistance and high transparency from a conventional ultraviolet-curable acrylic material. However, due to its large curing shrinkage percentage, the obtained lens is inferior in dimensional stability and may be involved in a problem such as generation of warpage. In addition, for example, a conventional epoxy resin composition has a high glass transition temperature and it is possible to obtain a lens molded article with excellent dimensional stability from a conventional epoxy resin composition. However, there may arise a problem that coloration readily occurs by heating.